Canine Urine Concentrating Test Guidelines

Notes:

Before testing dogs with reported severe polydipsia for Diabetes Insipidus (central or peripheral), primary polydipsia and renal medullary wash-out, the following protocol is recommended:

• Confirmation by a water intake test of an intake of > 90 ml/kg/day.
• Profile +/- further endocrine testing to rule out other identifiable causes of polydipsia/polyuria. This should include urea, creatinine, total protein, albumin, globulin, liver enzymes, bile acids, glucose, calcium, phosphate and electrolytes. If there is any suspicion of Cushing's, a screening test is advisable (Low Dose Dexamethasone Suppression, ACTH—separate protocols available on request).
• Urinalysis, including a dipstick, deposit examination and specific gravity determined by refractometer.
• These routine tests are included in the Geriatric 1 profile (which is also a PD/PU profile) and require submission of an EDTA, separated serum, fluoride blood samples and a plain urine.

NB: urine concentrating tests are frequently contraindicated in true geriatric dogs because of the age-associated loss of concentrating ability and the resulting loss of renal reserve capacity. Urine SG >1.030 in dogs (and >1.035 in cats) is an indication of adequate concentrating ability and no further testing is required. If polydipsia is confirmed and screening tests have failed to identify the cause, there may be indications for performing a urinary concentrating test. This test is usually performed in 2 phases:

PHASE 1: Responsiveness to Endogenous ADH

Protocol:

• 1. Empty urinary bladder (spontaneous micturition/catheterisation).
• 2. Weigh accurately.
• 3. Discontinue food and water.
• 4. Weigh every 2 hours and obtain urine to determine specific gravity.
• 5. Continue the test to 5% loss of total body weight.
• 6. Note the time to 5% loss and urine specific gravity at that time.

NB: The 5% level of dehydration must not be exceeded if pre-renal failure is to be avoided.

PHASE 2: Responsiveness to Exogenous ADH

1. If central Diabetes Insipidus is suspected, response to DD AVP, 1-4 drops in the conjunctival sac for 5-7 days is assessed by daily monitoring of urine specific gravity.

2. To rule out medullary wash-out—water consumption is gradually reduced to 60 ml/kg/day and the food lightly salted for 10-14 days to help re-establish medullary hyperosmolality. It is important that there be no reduction in bodyweight during this time which could reflect dehydration. Therefore, monitoring over this time is advisable. Water restriction should be discontinued if there is any change that might suggest dehydration with the consequent risk of pre-renal failure.

The initial response for Phase 1 (and also to Phase 2) can then be re-evaluated. Where wash-out is strongly suspected, it may be worth initiating this partial water deprivation period before testing further. In cases of wash-out alone, this intervention will be therapeutically helpful. In other cases, it will avoid the necessity of repeat testing.